1. Technical Field
The present invention relates to a method for bonding wafers and a structure of a bonding part, and more particularly, to a method for bonding two wafers by AuSn eutectic bonding and a structure of its bonding part.
2. Related Art
When bonding parts of two wafers are bonded, AuSn eutectic bonding is used in some cases. The AuSn eutectic bonding means a bonding method using an eutectic reaction of a metal and AuSn and is used in fields of advanced MEMS packaging and three-dimensional stacking technique. According to the AuSn eutectic bonding, the AuSn is melted like a solder, and it has an advantage that bonding can be easily performed even when a surface of the bonding part is rough like a plated layer.
Thus, when the bonding parts of the wafers are bonded by the AuSn eutectic bonding, as for one wafer, an adhesive layer formed of Cr is provided in some cases as a layer (lowermost layer) which is in contact with the wafer (refer to patent document 1). This adhesive layer functions to enhance adhesiveness between the bonding part and the wafer.
However, when the molten AuSn solder comes in contact with the adhesive layer and the AuSn diffuses into the adhesive layer when the bonding parts are bonded, adhesive force between the adhesive layer and the wafer deteriorates, and reliability reduces in the bonding part.
In addition, as for the other wafer, a penetration wiring which penetrates the wafer is connected in some cases to the bonding part (electrode) provided on a surface of the wafer (refer to patent document 2). In this case, the bonding part is previously provided on the surface of the wafer, a via hole is formed in the wafer so as to penetrate it, the penetration wiring is formed in the via hole by a plating method, and the penetration wiring is bonded to the bonding part. However, the bonding part is formed of the same material (such as Al) as the penetration wiring in the via hole in general, so that when the via hole is formed by etching the wafer, or when the penetration wiring is formed by plating, the bonding part could be etched and damaged by an etching solution or a plating solution (acid liquid in general).
[Patent Document 1]: Japanese Patent No. 3303227
[Patent Document 2]: Japanese Unexamined Patent Publication No. 2007-311771